fix(cli): make Ctrl+Enter insert newline on WSL/SSH/Windows Terminal (#22777)

Native Windows, WSL, SSH sessions, and Windows Terminal all send
Ctrl+Enter as bare LF (c-j). Hermes was binding c-j as submit on
every POSIX platform, so Ctrl+Enter submitted instead of inserting
a newline on those terminals. Reported in #22379.

Add _preserve_ctrl_enter_newline() predicate that detects the
environments where Ctrl+Enter must produce a newline (sys.platform
== 'win32', SSH_CONNECTION/SSH_CLIENT/SSH_TTY env, WT_SESSION,
WSL_DISTRO_NAME, /proc/version 'microsoft' marker). Gate the
c-j-as-submit binding off in those environments and gate the
c-j-as-newline handler on. Local POSIX TTYs without those markers
(docker exec, plain ssh from a Mac) keep c-j as submit so plain
Enter still works on thin PTYs.

Add install_ctrl_enter_alias() in hermes_cli/pt_input_extras.py
mapping the three CSI-u / modifyOtherKeys variants of Ctrl+Enter
('\x1b[13;5u', '\x1b[27;5;13~', '\x1b[27;5;13u') to the
(Escape, ControlM) tuple Alt+Enter produces. This lets Kitty /
mintty / xterm-with-modifyOtherKeys users over SSH get a Ctrl+Enter
newline through the existing Alt+Enter handler.

9 new tests + extended existing test_lf_enter_binds_to_submit_handler_posix
to cover bare-local vs SSH branches.

Closes #22379.

tests/cli/test_ctrl_enter_newline.py

@@ -0,0 +1,105 @@
+"""Regression tests for issue #22379 — Ctrl+Enter newline over SSH/WSL.
+
+prompt_toolkit treats c-j (LF) as Enter on POSIX so thin PTYs (docker exec,
+some BSD ssh) that send LF for plain Enter still work. But Windows Terminal
+(native, WSL, and SSH-forwarded sessions) sends Ctrl+Enter as bare LF — same
+byte. Without environment-aware gating, binding c-j to submit means
+Ctrl+Enter submits instead of inserting a newline.
+
+These tests pin the gating predicate and the resulting binding behavior.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+from unittest.mock import patch
+
+
+def test_native_windows_preserves_newline():
+    import cli as cli_mod
+    with patch.object(sys, "platform", "win32"):
+        assert cli_mod._preserve_ctrl_enter_newline() is True
+
+
+def test_ssh_session_preserves_newline_on_linux():
+    import cli as cli_mod
+    with patch.object(sys, "platform", "linux"):
+        with patch.dict(os.environ, {"SSH_CONNECTION": "1.2.3.4 5 6.7.8.9 22"}, clear=False):
+            assert cli_mod._preserve_ctrl_enter_newline() is True
+
+
+def test_ssh_tty_alone_preserves_newline():
+    import cli as cli_mod
+    with patch.object(sys, "platform", "linux"):
+        # Strip out anything that might leak truth
+        with patch.dict(os.environ, {"SSH_TTY": "/dev/pts/0"}, clear=True):
+            assert cli_mod._preserve_ctrl_enter_newline() is True
+
+
+def test_wsl_distro_name_preserves_newline():
+    import cli as cli_mod
+    with patch.object(sys, "platform", "linux"):
+        with patch.dict(os.environ, {"WSL_DISTRO_NAME": "Ubuntu-Microsoft"}, clear=True):
+            assert cli_mod._preserve_ctrl_enter_newline() is True
+
+
+def test_windows_terminal_session_preserves_newline():
+    import cli as cli_mod
+    with patch.object(sys, "platform", "linux"):
+        with patch.dict(os.environ, {"WT_SESSION": "abc-def"}, clear=True):
+            assert cli_mod._preserve_ctrl_enter_newline() is True
+
+
+def test_pure_local_linux_does_not_preserve():
+    """A bare local Linux TTY (no SSH/WSL/WT) keeps c-j → submit so docker exec
+    style Enter-as-LF stays usable."""
+    import cli as cli_mod
+    # Stub out /proc reads — those are the WSL fallback signal.
+    with patch.object(sys, "platform", "linux"):
+        with patch.dict(os.environ, {}, clear=True):
+            with patch("builtins.open", side_effect=OSError("no /proc")):
+                assert cli_mod._preserve_ctrl_enter_newline() is False
+
+
+def test_proc_version_microsoft_marker_preserves_newline():
+    """WSL detection via /proc when env vars are scrubbed (sudo etc.)."""
+    import cli as cli_mod
+    from io import StringIO
+    with patch.object(sys, "platform", "linux"):
+        with patch.dict(os.environ, {}, clear=True):
+            real_open = open
+            def _fake_open(path, *args, **kwargs):
+                if "/proc/version" in str(path) or "/proc/sys/kernel/osrelease" in str(path):
+                    return StringIO("Linux version 5.15.167.4-microsoft-standard-WSL2")
+                return real_open(path, *args, **kwargs)
+            with patch("builtins.open", side_effect=_fake_open):
+                assert cli_mod._preserve_ctrl_enter_newline() is True
+
+
+# ---------------------------------------------------------------------------
+# install_ctrl_enter_alias() — ANSI sequence mappings for enhanced terminals
+# ---------------------------------------------------------------------------
+
+
+def test_install_ctrl_enter_alias_maps_csi_u_sequences():
+    """Kitty / xterm modifyOtherKeys / mintty Ctrl+Enter sequences alias to
+    Alt+Enter (Escape, ControlM) so the existing newline handler fires."""
+    from hermes_cli.pt_input_extras import install_ctrl_enter_alias
+    from prompt_toolkit.input.ansi_escape_sequences import ANSI_SEQUENCES
+    from prompt_toolkit.keys import Keys
+
+    install_ctrl_enter_alias()
+    alt_enter = (Keys.Escape, Keys.ControlM)
+    for seq in ("\x1b[13;5u", "\x1b[27;5;13~", "\x1b[27;5;13u"):
+        assert ANSI_SEQUENCES.get(seq) == alt_enter, (
+            f"Ctrl+Enter sequence {seq!r} not mapped to Alt+Enter tuple"
+        )
+
+
+def test_install_ctrl_enter_alias_idempotent():
+    """Running it twice doesn't double-count or break."""
+    from hermes_cli.pt_input_extras import install_ctrl_enter_alias
+    install_ctrl_enter_alias()
+    second = install_ctrl_enter_alias()
+    assert second == 0  # no further changes after first install